Wiskott-Aldrich Syndrome (WAS) is an X-linked immunodeficiency caused by mutations that affect the WAS protein (WASP). It is characterized by thrombocytopenia, eczema, impaired immunity and a predisposition to develop lymphomas and leukemias (Cooper, M. D., Chase, H. P., Lowman, J. T., Krivit, W. & Good, R. A. (1968) Am. J. Medicine, 44: 499-513). The size of platelets and lymphocytes is reduced in WAS and scanning electron microscopy of T lymphocytes shows a relatively smooth surface with decrease in the number and size of microvilli, suggesting a defect in cytoskeletal architecture (Remold-O'Donnell, E. & Rosen, F. S. (1993) in Sialophorin (CD43) and the Wiskott-Aldrich Syndrome, eds. Rosen, F. S. & Seligmann, M. S. (Harwood Academic Publishers, Chur), pp. 225-241), pp.225-241 (1993)). The WAS gene is located on Xp11.22-Xp11.23 and encodes a 502 amino acid (aa) long proline rich protein, WASP (Derry, J. M. J., Ochs, H. D. & Francke, U. (1994) Cell, 78: 635-644.). WASP contains an N-terminal pleckstrin homology (PH) domain, which partially overlaps with a WASP homology (WH) domain, WH1, found in several proteins involved in the maintenance of cytoskeletal integrity that include Ena, Mena, Evl and VASP (Gertler, F. B., Niebuhr, K., Reinhard, M., Wehland, J. & Soriano, P. (1996) Cell, 87: 227-239). The WH1 domain in WASP is followed by a GTPase binding domain (GBD/CRIB) (Bunnell, S. C., Henry, P. A., Kolluri, R., Kirchhausen, T., Rickles, R. J. & Berg, L. J. (1996) J. Biol. Chem. 271: 25646-25656), a number of proline rich stretches, a second WH domain (WH2), a short verprolin homology sequence, a cofilin homology sequence, and an acidic C-terminal region. Recently, a protein highly homologous to WASP was cloned from bovine brain and was termed N-WASP (Miki, H., Miura, K. & Takenawa, T. (1996) EMBO J. 15, 5326-5335). N-WASP has a domain organization similar to that of WASP, and is widely expressed, in contrast to WASP which is expressed only in hematopoietic cells.
WASP binds via its GBD domain to the small molecular weight GTPase Cdc42 and weakly to Rac, but not to Rho (Aspenstrom, P., Lindberg, U. & Hall, A. (1996) Curr. Biol. 6: 70-75; Kolluri, R., Tolias, K. F., Carpenter, C. L., Rosen, F. S. & Kirchhausen, T. (1996) Proc. Natl. Acad. Sci. (USA) 93: 5615-5618; Symons, M., Derry, J. M. J., Kariak, B., Jiang, S., Lemahieu, V., McCormick, F., Francke, U. & Abo, A. (1996) Cell 84: 723-734). Cdc42, Rac and Rho regulate cytoskeletal organization (Nobes, C. D. & Hall, A. (1995) Cell 81: 53-62). Overexpression of WASP induces the formation of actin-containing clusters (Symons, M., Derry, J. M. J., Kariak, B., Jiang, S., Lemahieu, V., McCormick, F., Francke, U. & Abo, A. (1996) Cell 84: 723-734). This is inhibited by dominant negative mutants of Cdc42, but not of Rac or Rho (Symons, M., Derry, J. M. J., Kariak, B., Jiang, S., Lemahieu, V., McCormick, F., Francke, U. & Abo, A. (1996) Cell 84: 723-734). These findings suggest that WASP may provide a link between Cdc42, Rac and the cytoskeleton.
WASP interacts with components of signal transduction pathways via their SH3 domains (Src homology 3) which recognize the proline rich domain in WASP (Featherstone, C. (1997) Science 275: 27-28). WASP associates with the adaptor protein Nck (Rivero-Lezcano, O. M., Marcilla, A., Sameshima, J. H. & Robbins, K. C. (1995) Mol. Cell Biol., 15: 5725-5731). Nck can be recruited via its SH2 domain to tyrosine phosphorylated receptors (Galisteo, M. L., Chernoff, J., Su, Y.-C., Skolnich, E. Y. & Schlessinger, J. (1996) J. Biol. Chem. 271: 20997-21000). WASP also binds in vivo to fyn (Rivero-Lezcano, O. M., Marcilla, A., Sameshima, J. H. & Robbins, K. C. (1995) Mol. Cell Biol. 15: 5725-5731; Banin, S., Truong, O., Katz. D. R., Waterfield, M. D., Brickell, P. M. & Gout, I. (1996) Curr. Biol., 6: 981-988) and in vitro to the src kinase fgr, to the tyrosine kinases btk, itk, Abl and to the p85 subunit of PLC-g (Banin, S., Truong, O., Katz. D. R., Waterfield, M. D., Brickell, P. M. & Gout, I. (1996) Curr. Biol. 6, 981-988; Molina, I. J., Sancho, J., Terhorst, C., Rosen, F. S. & Remold-O'Donnell, E. (1993) J. Immunol., 151: 4383-4390; Finan, P. M., Soames, C. J., Wilson, L., Nelson, D. L., Stewart, D. M., Truong, O., Hsuan, J. J. & Kellie, S. (1996) J. Biol. Chem., 271: 26291-26295).
The WASP-interacting protein (WIP) is a proline-rich protein. However, the role of WIP in TCR-mediated cell activation and cytoskeleton organization are not understood.
There exists a need therefore, for further studies, particularly in vivo studies, to elucidate the biological functions of WIP, to identify regulators of WIP, and to develop therapeutic strategies for the treatment or prevention of diseases or conditions that are associated with WIP function.